The lactate concentration in the blood is one of the important substances formed during an exercise and the formation is depending on the athlete's cardio respiratory fitness. It is used to determine the transition between the aerobic and anaerobic energy delivery system (=lactate threshold). The lactate threshold (LT) or anaerobic threshold (i.e., the point at which the subject can no longer provide all of the energy necessary to perform that workload with only aerobic metabolism) or more specifically, the maximal lactate steady state (MLSS) is a measure for the current cardio respiratory fitness of the individual athlete. It is defined as the highest exercise intensity that can be maintained for extended periods of time. At exercise intensities above the anaerobic threshold, carbohydrates are anaerobically metabolized into lactic acid, as opposed to pyruvate under aerobic metabolism. While the body is able to clear (i.e., metabolize) some lactic acid, a point is eventually reached whereby the lactic acid begins to accumulate in the muscles and bloodstream, eventually causing muscle soreness and fatigue.
Knowledge of the transition between the aerobic and the anaerobic training zone is an essential aspect in many training protocols and for monitoring the total training intensity, including in training protocols for amateur athletes or professional athletes, in exercise schedules in fitness centres or in the rehabilitation process of many thousands of patients. Long training sessions in the anaerobic training zone will impose a heavy training load on the athlete. This means that he will not be able to sustain this training level for a long time. This is unwanted particularly during endurance training. Endurance training protocols generally comprise of long hours of exercise at an aerobic level. A simple, yet accurate, method for monitoring the exercise level will be a great addition to training soft- and hardware, because it makes training protocols, where a clear distinction between aerobic and anaerobic training zones is necessary, easier to complete.
Today, the numbers of entries in the fitness centres are skyrocketing. The reason is the experience of the positive impact of a healthy body on the quality of life (Mens sana in corpore sano). Many people are forced to follow that rule, because they suffer from disease of civilization such as obesity, cardiovascular diseases . . . . However, not many people from that large group complete their exercise, because their busy schedule does not allow for extensive exercise schedules in fitness centres or because their condition is not improving fast enough for them to notice. This is due to the fact that the exercise schedules do not target the individual. Individual exercise guidance will lead to a shorter workout with better results, making the people more inclined to finish the exercise. This gives people also more perseverance, because the exercise is specifically made for them instead for another. To optimize their individual exercise, an accurate estimate of their cardio respiratory fitness is necessary. The test should be simple and short, so that they can perform the test each day before the exercise and preferably during the warming-up.
Different types of exercise also play an important role in the rehabilitation process of many thousands of patients (Expenditure of the Belgian RIZIV 2008: 340 Million Euro, http://riziv.fgov.be), and the specific physical guidance of a significant group of physically disabled people. Currently, the majority of those patients go through (depending on the disorder) empirical standard therapeutic exercise regimens in which limited attention is given to their individual response to exercise. The cost of rehabilitation is substantial, so that significantly shorter and optimal rehabilitation will be cost efficient for the health insurance. Some specific rehabilitation protocols that use ergo meters can be optimized if the current cardio respiratory fitness can be determined in a correct and easy way.
Determination of Cardio Respiratory Fitness
Many tests to assess the cardio respiratory fitness of people are known.
Many amateur athletes use predefined heart rate levels to train. These levels are defined in percentages of their maximal heart rate (HRMax). The common rule to define the HRMax is:HRMax=220−age,but also other generic rules are used.
However, these rules are established at population level. They lead to exercise protocols which are far from optimal, because they do not take the individual and time-variant aspect of cardio respiratory fitness into account.
Professional athletes actually measure their cardio respiratory fitness by measuring their LT with a step test until exhaustion. This test is currently regarded as the reference measurement for determining cardio respiratory fitness. This test is very comprehensive and requires expertise to implement, because lactate measurements should be executed. The earlobe is pricked in this invasive test to obtain a droplet of blood in which the lactate concentration is determined. This test is only performed a few times a year (every four to six weeks), because it has negative effects on the body of the professional athlete if the test is performed too often. The problem is that the cardio respiratory fitness can vary in the period between two of those tests.
The LT is an important variable in sports physiology. The LT is well documented in the literature, but is defined in many different ways. The only accurate way to determine the LT is to measure the MLSS. This requires several exercise tests performed over a span of 1 to 2 weeks [Van Schuylenbergh, et al., International Journal of Sports Medicine, 2004, 25(6), 403-408]. This is a very elaborate process and impractical for professional athletes. Therefore many sports physiologists try to estimate the LT with other physiological variables that are easier to measure. For this purpose lactate and respiratory measurements are used. Conconi [Conconi et al., Journal of Applied Physiology, 1982, 52(4), 869-873] developed a non invasive test for determining the anaerobic threshold for runners. He used the inflection point in the relationship between speed and heart rate during running as estimator for the anaerobic threshold. This study was repeated for cyclists, where the relationship between power and heart rate was used [Grazzi et al., Medicine and Science in Sports and Exercise, 1999, 31(10) 1478-1483]. The Conconi test is widely used although the test is very controversial, because a clear inflection point is not always observed. Furthermore, the inflection point depends on the test protocol.
Sub-maximal tests are also used to estimate the cardio respiratory fitness, but they are not as accurate as the step test until exhaustion.
Some fitness systems use a measured or estimated physical parameter to control the exercise (US2009/0312150, WO2009/133248). They control the exercise by linking the relative intensity of an exercise to the physical parameter, namely the heart rate, in order to obtain an optimal exercise level. However, current state-of-art does not take into account that the physical response to exercise intensity is individually different for every individual. This could cause problems when exercise protocols are made. Also, current state-of-art does not use the absolute exercise intensity indicator. So, the exercise intensity could be over- or under-estimated, which will resolve in inefficient exercise protocols.
EP1127543 describes method and systems to assess the lactate concentration in a human body in connection with exercise using a mathematical model, implemented as a neural network which relates heart rate information with lactate concentration by a stress level, defined as the quantity of performed exercise intensity during the last hour. Since training using data from many hundreds or thousands of persons is an essential feature of this neural network, this method again is based on on statistical relationships taken from a population of many individuals. In reality however no living organism is acting or behaving as an average of a population, but instead as an individual, dynamic and time-varying system, which does not respond in a standard way. A neural network solution can hence never be more accurate than the standard deviation around the theoretical average and for living organisms this ends up in a high error for each individual at a given moment.
Thus, the currently used tests to determine cardio respiratory fitness or measure exercise intensities are often elaborate and/or inaccurate, are insufficiently adapted to the individual training person or are difficult to use in real-time. Indeed, the lactate threshold is varying in time for an individual, depending on his physical condition.
Thus, there is a need in the art for a more accurate, simpler, short, individualised exercise system and control method thereof that monitors, determines and estimates or predicts the transition between the aerobic and anaerobic training zone, and thus also the cardio respiratory fitness.